1. Field of the Invention
This invention generally relates to a data processing circuit and method for a liquid crystal display and, more particularly, to a pixel data preprocessing circuit and method.
2. Description of the Related Art
The operating principle of a liquid crystal display is to control the arrangement of liquid crystal molecules sandwiched between two transparent substrates by adjusting the bias applied to the two transparent substrates thereby correspondingly controlling the amount of penetrated light within each pixel area so as to show images on the display. In recent years, accompanying with the increase of the resolution of liquid crystal displays, the data rate of pixel data is correspondingly increased thereby increasing the access speed of a frame memory to generate serious electromagnetic interference (EMI) problems.
In addition, as the response of liquid crystal molecules following the electric field applied thereto can not keep pace with the change of electric field itself, the liquid crystal display will appear image sticking during displaying dynamic images thereby decreasing the image quality. In order to solve this problem, the field of art has proposed an overdrive method, i.e. a voltage level larger than the desired gray level value is applied to liquid crystal molecules during gray level transition so as to reduce the required time for rearranging liquid crystal molecules. In the meantime, an overdrive lookup table is formed by recording gray level values of a current frame and its previous frame such that an overdrive voltage to be outputted to the source driver can be determined according to the lookup table during gray level transitions. For example, Taiwan Patent No. I282544 discloses an operation apparatus for overdrive and operation method for overdrive that determines an overdrive voltage to be outputted according to an overdrive lookup table.
Please refer to FIG. 1, it shows a conventional overdrive method including the following steps. The timing controller 910 inputs a current pixel data F(N+1,M) to a comparator 911 and a frame memory 920. The timing controller 910 reads a previous pixel data F(N,M) from the frame memory 920. The comparator 911 obtains an overdrive pixel data F′(N+1,M) from the lookup table 930 based on the current pixel data F(N+1,M) and the previous pixel data F(N,M). And the overdrive pixel data F′(N+1,M) is inputted into a source driver 21 and a gate driver 22 of a liquid crystal display 2 so as to display images on a liquid crystal panel 23; wherein the current pixel data F(N+1,M) is the Mth row of pixel data of the (N+1)th frame; the previous pixel data F(N,M) is the Mth row of pixel data of the Nth frame; and the overdrive pixel data F′(N+1,M) is the Mth row of overdrive pixel data of the (N+1)th frame for driving a row of pixels of the liquid crystal panel 23 through the source driver 21.
Please refer to FIG. 2, it shows a distribution of the pixel data of a 7×8 frame F, wherein when the first row of pixel data of the frame F are going to be stored into or read out from the frame memory 920, the storing and reading processes may be started from the most left pixel data of the frame F to the right to sequentially store every pixel data in the first row into the frame memory 920 or to sequentially read every pixel data in the first row from the frame memory 920, i.e. the pixel data will be stored into the frame memory 920 or read out from the frame memory 920 in a sequence of 01010 . . . . The data change between two adjacent pixels will generate electromagnetic interference during accessing the frame memory 920. As mentioned above, with the increase of speed for accessing the frame memory, this kind of electromagnetic interference problem during accessing the frame memory will become more serious.